1. Field of the Invention.
The present invention relates to the field of angioplasty. In particular, the present invention relates to a balloon catheter which provides prolonged dilatations without blocking blood flow by use of passive perfusion.
2. Description of the Prior Art.
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating types of vascular diseases. In particular, angioplasty is widely used for opening stenoses in coronary arteries, although it is also used for treatment of stenoses in other parts of the vascular system. The most widely used form of angioplasty is called percutaneous transluminal coronary angioplasty (PTCA) and makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying fluid under pressure through an inflation lumen to the balloon. The inflation of the balloon opens the artery to reestablish acceptable blood flow through the artery.
An initial concern about PTCA was the temporary blockage of blood flow during balloon inflation. As cardiologists gained clinical experience with PTCA, the concern with temporary blood flow blockage declined; the vast majority of patients tolerate 30 to 60 second dilatations quite well. Concurrently, cardiologists discovered that prolonged dilatations can help overcome certain kinds of complications encountered with the angioplasty. Prolonged dilatations of several minutes are used to deal with dissections, intimal flaps, acute thrombosis and vessel spasms. The profound ischemia of a long dilatation is outweighed by the potential prevention of emergency coronary bypass surgery.
In the prior art, methods for enabling prolonged dilatations have been cumbersome, have been experimental, or have had potentially harmful side effects. Consequently, there has been no definitive study of the effects of prolonged dilations on the efficacy of PTCA.
In order to perform prolonged dilatations, several approaches have been suggested. These include the use of pharmacologic agents to improve myocardial tolerance of ischemia, synchronized retroprofusion, mechnical pump distal perfusion, and auto or passive perfusion.
The use of pharmacologic agents treats the symptoms of ischemia, but not the cause. As a result, this approach is inherently limited.
Synchronized retroprofusion involves pumping blood during diastole into the coronary sinus and then subselectively into the regional coronary veins which drain the jeopardized myocardium. This approach potentially offers nearly complete myocardial perfusion. The disadvantage of synchronized retroprofusion, however, is that it is complicated and cumbersome.
Mechanical pump distal perfusion involves pumping blood (or other perfusate) through a lumen of the PTCA catheter. The need to pump through the PTCA catheter requires some form of mechanical pump, and complicates the angioplasty equipment and procedure.
With passive perfusion, the balloon catheter acts as a temporary stent. Passive or auto perfusion catheters which have been proposed in the past have used a design similar to "bail out" catheters: side holes in the catheter through-lumen proximal and distal to the balloon. These catheters, however, have several limitations. First, blood flow through the balloon may be suboptimal for many clinical situations (such as distal lesions and hypotension). Second, this configuration presents the problem of catheter initiated thrombus, for which no satisfactory solution has emerged. Third, the crossing profiles of these catheters typically require two step angioplasty--the lesion is first opened with a low profile catheter, which then must be exchanged with a perfusion balloon for a long dilatation period.